M.S.
Have you thought about making her bedroom more inviting? My sister had problems with her 3 year old daughter staying in her own bed until they moved (I'm not suggesting you move). Anyway, her daughter got to choose the paint color,new comfortable cover, pillows, etc. They even repainted her toddler bed. Somehow this did the trick. It was slow a slow transistion at first (she would still want to crawl into bed with her parents). But, she got the idea that she was a big girl and had a big girl room that she really felt was hers.